Word Processing systems have been developed employing distributed processing. One word processing system employs microcomputers to implement distributed intelligence in multiple station systems.
In multiple user systems of the type described in co-pending appliction, Ser. No. 177,531 filed concurrently herewith and entitled "Word Processing System Employing a Plurality of General Purpose Processor Circuits" for Johnson, Frediani and Lillie and assigned to the present assignee, it is necessary to provide a means for the various subsystems to communicate. Communications among the subsystems enables the various functions to be partitioned between the subsystems and allows the resources of the system to be shared effectively.
Various communication systems are usable in distributed processing subsystems. One such system is shown in U.S. Pat. No. 3,815,104 granted to Goldman. In this system, subsystems are hard wired and each dedicated to a particular task. FIG. 1 in this reference, for example, clearly indicates that hardware is associated with each function such as pagination, justification, clean up hyphen and keyboard interface. Thus, flexibility is very much constrained in terms of the hardware of the system. Each subsystem includes a display, a memory and a manually operable keyboard for entering data and control commands. The subsystems are connected to each other by means of a communications bus which includes a data bus, a special control and indicator bus, an address bus and a timing bus. Although the system utilizes distributed processing, each subsystem is rigid in that its function is designed into the hardware and it is not capable of being utilized for any other function. Moreover, each subsystem can communicate only during the time allocated by the multiplex arrangement. As a result, there is limited flexibility in the communications capability and the system is time limited in that only a narrow window of time is available for communication among subsystems by any particular subsystem.
Communications systems have been developed involving memory mapping. One such system has been developed by the Intel Corporation. This communication system is described in Intel Application Note AP-28A entitled "Multibus Interfacing".